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1 /*	$OpenBSD: ungetc.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */
2 /*-
3  * Copyright (c) 1990, 1993
4  *	The Regents of the University of California.  All rights reserved.
5  *
6  * This code is derived from software contributed to Berkeley by
7  * Chris Torek.
8  *
9  * Redistribution and use in source and binary forms, with or without
10  * modification, are permitted provided that the following conditions
11  * are met:
12  * 1. Redistributions of source code must retain the above copyright
13  *    notice, this list of conditions and the following disclaimer.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice, this list of conditions and the following disclaimer in the
16  *    documentation and/or other materials provided with the distribution.
17  * 3. Neither the name of the University nor the names of its contributors
18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  */
33 
34 #include <stdio.h>
35 #include <stdlib.h>
36 #include <string.h>
37 #include "local.h"
38 
39 static int __submore(FILE *);
40 /*
41  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
42  * the buffer moves, so that it points the same distance from the end,
43  * and move the bytes in the buffer around as necessary so that they
44  * are all at the end (stack-style).
45  */
46 static int
__submore(FILE * fp)47 __submore(FILE *fp)
48 {
49 	int i;
50 	unsigned char *p;
51 
52 	if (_UB(fp)._base == fp->_ubuf) {
53 		/*
54 		 * Get a new buffer (rather than expanding the old one).
55 		 */
56 		if ((p = malloc((size_t)BUFSIZ)) == NULL)
57 			return (EOF);
58 		_UB(fp)._base = p;
59 		_UB(fp)._size = BUFSIZ;
60 		p += BUFSIZ - sizeof(fp->_ubuf);
61 		for (i = sizeof(fp->_ubuf); --i >= 0;)
62 			p[i] = fp->_ubuf[i];
63 		fp->_p = p;
64 		return (0);
65 	}
66 	i = _UB(fp)._size;
67 	p = realloc(_UB(fp)._base, i << 1);
68 	if (p == NULL)
69 		return (EOF);
70 	/* no overlap (hence can use memcpy) because we doubled the size */
71 	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
72 	fp->_p = p + i;
73 	_UB(fp)._base = p;
74 	_UB(fp)._size = i << 1;
75 	return (0);
76 }
77 
78 int
ungetc(int c,FILE * fp)79 ungetc(int c, FILE *fp)
80 {
81 	if (c == EOF)
82 		return (EOF);
83 	if (!__sdidinit)
84 		__sinit();
85 	_SET_ORIENTATION(fp, -1);
86 	if ((fp->_flags & __SRD) == 0) {
87 		/*
88 		 * Not already reading: no good unless reading-and-writing.
89 		 * Otherwise, flush any current write stuff.
90 		 */
91 		if ((fp->_flags & __SRW) == 0)
92 			return (EOF);
93 		if (fp->_flags & __SWR) {
94 			if (__sflush(fp))
95 				return (EOF);
96 			fp->_flags &= ~__SWR;
97 			fp->_w = 0;
98 			fp->_lbfsize = 0;
99 		}
100 		fp->_flags |= __SRD;
101 	}
102 	c = (unsigned char)c;
103 
104 	/*
105 	 * If we are in the middle of ungetc'ing, just continue.
106 	 * This may require expanding the current ungetc buffer.
107 	 */
108 	if (HASUB(fp)) {
109 		if (fp->_r >= _UB(fp)._size && __submore(fp))
110 			return (EOF);
111 		*--fp->_p = c;
112 		fp->_r++;
113 		return (c);
114 	}
115 	fp->_flags &= ~__SEOF;
116 
117 	/*
118 	 * If we can handle this by simply backing up, do so,
119 	 * but never replace the original character.
120 	 * (This makes sscanf() work when scanning `const' data.)
121 	 */
122 	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
123 	    fp->_p[-1] == c) {
124 		fp->_p--;
125 		fp->_r++;
126 		return (c);
127 	}
128 
129 	/*
130 	 * Create an ungetc buffer.
131 	 * Initially, we will use the `reserve' buffer.
132 	 */
133 	fp->_ur = fp->_r;
134 	fp->_up = fp->_p;
135 	_UB(fp)._base = fp->_ubuf;
136 	_UB(fp)._size = sizeof(fp->_ubuf);
137 	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
138 	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
139 	fp->_r = 1;
140 	return (c);
141 }
142